1. Field of the Invention
This invention relates to certain activator precursor compounds, especially activator-stabilizer precursor compounds, for use in photographic materials for processing with heat. More particularly, this invention relates to such compounds wherein the acid portion of the compound is a 2-carboxycarboxamide. One aspect of the invention relates to heat developable and heat stabilizable photographic elements comprising the described 2-carboxycarboxamide compounds. Another aspect relates to photographic compositions for processing with heat containing these compounds. A further aspect relates to a heat activatable photographic processing composition containing the described activator precursors, especially activator-stabilizer precursors.
2. Description of the State of the Art
It is known to provide photographic elements that are heat processable, particularly heat developable. That is, photographic elements are known wherein a latent image can be developed by heating the element. Typically, such elements contain photosensitive silver halide, a silver halide developing agent, a developing agent activator precursor and, typically, a stabilizer precursor to provide improved stability to the developed image. Upon development by application of heat, the developer, activator and stabilizer are released from their respective precursors. Development of the latent image and stabilization occur substantially simultaneously as the result of two competing reactions. It is necessary to provide an activator precursor, particularly an activator-stabilizer precursor, that permits the respective reactions to take place without adversely affecting the desired sensitometric properties of the element.
A heat developable photographic element is known wherein an image is developed, for example, by a developing agent that is activated by the decarboxylation products of organic acids. This is described, for example, in U.S. Pat. No. 3,220,846 of Sagura and Tinker, issued Nov. 30, 1965. An example of such a heat developable photographic material contains piperidine trichloroacetate that decarboxylates upon heating to provide piperidine, carbon dioxide and chloroform. The piperidine activates the developing agent in the photographic material while the chloroform, that is volatile at processing temperatures, and the carbon dioxide are released into the binder of the photographic material. This release of gases is often undesirable, particularly in microimaging.
Other heat developable photographic and, in some cases, heat stabilizable photographic materials are described, for instance, in U.S. Pat. No. 3,301,678 of Humphlett, Johnson and Haist, issued Jan. 31, 1967; British Patent No. 1,161,777 published Aug. 20, 1969; U.S. Pat. No. 3,152,904 of Sorenson et al, issued Oct. 13, 1964; British Patent No. 1,131,108 published Oct. 23, 1968; U.S. Pat. No. 3,392,020 of Yutzy et al, issued July 9, 1968; German Patent No. 888,045 published Aug. 27, 1953; and British Patent No. 930,572 published July 3, 1963. Use of base-release agents, or activator precursors, is described in certain of these heat processable photographic materials.
It is known to incorporate stabilizer precursors in heat developable photographic materials. Certain sulfur-containing compounds can be heat activated to release a stabilizing moiety in the photographic materials. This is described, for example, in U.S. Pat. No. 3,301,678 of Humphlett, Johnson and Haist, issued Jan. 31, 1967. It is believed that the sulfur-containing stabilizer precursor breaks down or "cleaves" at processing temperatures to provide a moiety that combines with the silver halide in the unexposed and undeveloped areas of the photographic material. The resulting silver mercaptide is more stable than silver halide to light, atmospheric and ambient conditions. Typically, the stabilizer precursors described are isothiuronium compounds.
Certain bis-isothiuronium compounds having an intermediate ureylene or ether moiety between isothiuronium moieties are also known as activator-stabilizers. These are described, for example, in U.S. Pat. No. 3,669,670 of Haist and Humphlett, issued June 13, 1972. Heating of these activator-stabilizer precursors releases both a development activator moiety and a stabilizer moiety. These compounds, however, have resulted in one or more disadvantages including: (1) the requirement of larger concentrations of processing chemicals than desired, (2) in many cases obnoxious odors upon heat processing, and (3) less than desired post-processing image stability.
In U.S. Ser. No. 551,182 of D. G. Dickerson and P. B. Merkel, filed Feb. 19, 1975 entitled "Activator-Stabilizers in Heat Developable Photographic Materials and Processes", now U.S. Pat. No. 4,012,260, and in Research Disclosure, Volume 140, Dec. 1975, Item 14049, published by Industrial Opportunities Ltd., Homewell, Havant, Hampshire, P09 1EF, UK, certain 2-amino-2-thiazolium carboxylates are described as activator-stabilizer precursors in heat processable photographic materials. Upon heating the photographic material containing these compounds, the activator-stabilizer precursors release an agent that is capable of activating a developing agent in the material. The precursors also release a moiety which is capable of stabilizing a silver halide image in the material. Although the described activator-stabilizer precursors are useful in heat developable photographic materials, these carboxylate compounds have certain drawbacks. The byproducts formed by the decarboxylation of the precursors are undesirably volatile at processing temperatures. These volatile byproducts are released into the photographic material along with carbon dioxide. Examples of the byproducts that are given off by certain of these activator precursors include chloroform, acetaldehyde and methyl cyanide. These compounds which can escape into the environment are highly toxic gases. In addition to their undesired toxicity, these gases along with carbon dioxide released by the decarboxylation can form undesirable bubbles in the heat processable photographic material. This is particularly disadvantageous in microfilm applications.
In copending application U.S. Ser. No. 712,459 of Merkel and Ling, filed Aug. 6, 1976 heat developable and heat stabilizable photographic silver salt materials are described containing an activator-stabilizer precursor having a base portion and an acid portion wherein the acid portion is an .alpha.-sulfonylacetate. Such activator-stabilizer precursors provide activation and stabilization without significant volatile byproducts of decarboxylation, except CO.sub.2. However, it has been noted that the compounds containing the .alpha.-sulfonylacetate do provide a disadvantage in that the photographic materials upon processing containing these activator stabilizers have what are described in the photographic art as "pinholes". "Pinholes" as described herein mean small areas of low density in the photographic material that can be readily observed visually through a 10X magnifying observation means. The "pinholes" are most readily apparent in the maximum density areas of the developed photographic material. The following comparative Example 3 illustrates a photographic material which contains undesirable "pinholes". Processed samples of the material, according to this example, contain roughly several hundred "pinholes" per square centimeter averaging approximately 0.05 millimeters in diameter. This property is particularly disadvantageous in microimaging.
Thus, there has been a continuing need for improved activator precursors, especially activator-stabilizer precursors that have byproducts which have reduced toxicity and volatility and reduce the number of undesired "pinholes" in heat processable photographic materials, especially those designed for microimaging. In addition, there has been a need to provide activator-stabilizer precursors in heat processable photographic materials which do not provide byproducts that contribute to bubble formation and also do not significantly adversely affect the desired sensitometric properties of the photographic material. The described art provides no guidance for the selection of an improved acid anion in an activator precursor, especially an activator-stabilizer precursor, in a heat processable photographic material that provides the desired combination of properties.